Switching power supplies or voltage regulators/converters are widely used in high power applications because of their high efficiency and the small amount of area/volume consumed by such regulators. Widely accepted switching voltage regulators include buck, boost, buck-boost, forward, flyback, half-bridge, full-bridge, and SEPIC topologies. Multiphase buck converters are particularly well suited for providing high current at low voltages needed by highly integrated electronic components such as microprocessors, graphics processors, and network processors. Buck converters are typically implemented with active components such as a pulse width modulation (PWM) controller IC (integrated circuit), driver, power MOSFETs (metal-oxide-semiconductor field-effect transistors), and passive components such as inductors, transformers or coupled inductors, capacitors, and resistors. Parallel converters are also used in applications where high current requirements can be met by connecting multiple output converters in parallel and applying current sharing between them to meet the total output current requirement. The terms ‘multiphase regulator’ and ‘parallel converter’ are used interchangeably herein, as are the terms ‘output phase’ and ‘output converter’.
Highly integrated electronic components typically require accurate voltage supplies capable of supplying large amounts of current and power, while maintaining tight voltage regulation and subject to tight implementation area constraints. A common power distribution scheme involves the use of an intermediate bus, where a higher voltage AC or DC bus is converted to an intermediate voltage, (e.g. 12V), and then multiple point-of-load voltage regulators are connected to this intermediate bus and step down the voltage to satisfy low voltage, high current demand of the electronic components. Multiphase buck converters are well suited for this sort of step down converter application, because multiphase buck converters are capable of supplying currents in excess of 50 A per phase at voltages below 1V, and are scalable by adding multiple phases in parallel and interleaving the operation of the phases. However, operating at low currents results in low efficiency as the power losses do not scale down as phase current decreases. Switching losses are the losses that occur due to high voltage and current experienced by the switch of a phase when transitioning from on to off state and vice-versa. Switching losses are insignificant at nominal to heavy loads, but at light load conditions, switching losses become more significant, reducing the efficiency of a multiphase converter system.
Proper power and heat management are critical to maximize system performance. This includes (a) maximizing both the peak instantaneous power delivered over a short duration (commonly referred to as burst or turbo mode operation) and the long-term time average power delivered over a longer duration, (b) maximizing the energy efficiency of the system, (c) powering system fan(s) to maintain component temperature within permitted operating limits, and (d) minimizing losses during low power operation such as in idle and sleep mode operation.
Multiphase buck converters which dynamically adjust the number of phases in operation, using phase shedding (dropping) techniques, are widely used to provide improved light load efficiency operation. This is particularly significant in systems where the load current is highly dynamic, bursty and variable over time. For example, in multicore and multiprocessor systems, it is generally preferable to fully load some processors while leaving other processors idle. In addition, it is preferable for cores to operate in a bursty, low latency manner, where high throughput processing is provided as soon as it is needed, and then resume idle or background operation after the task is completed.
In an intermediate bus type architecture, it is desirable to minimize both power and current capability of the intermediate bus, so that the intermediate bus can provide the time-average power needs, but not necessarily the worst-case peak power needs, so as to minimize power supply cost. However, this leaves the system vulnerable to operational failure when the power supply fails to deliver the necessary instantaneous power demand of the system.
A solution which maximizes the peak and average power demand, while also providing efficient light load operation, robust operation under peak load condition, and minimizing system cost is desirable.